As semiconductor devices shrink, there is a desire to decrease the area occupied by features, such as capacitors. To accommodate, capacitors are being formed over transistors (e.g., at the metal level) as opposed to being formed at the transistor level closer to the bulk semiconductor substrate. One example of such a capacitor is a metal-insulator-metal (MIM) capacitor which includes a MIM dielectric between a top electrode and a bottom electrode.
The metal layers may be formed using aluminum, copper, or alloys thereof. Typically, a capping layer or anti-reflective coating (ARC) is formed over the metal layers and can be used as the bottom electrode for the MIM capacitor being formed over the metal layers. In the industry, one such ARC material is TiN. While using the ARC as a bottom electrode is desirable for processing simplicity, the surface of the TiN in contact with the MIM dielectric is rough. The rough surface of the TiN creates geometrically enhanced fields which degrade the reliability of the MIM dielectric. Thus, a need exists to control the uniformity of the electric field especially when using TiN as an electrode in a MIM capacitor.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.